Exploding squirted wire pulsed light squrce



Dec. 29, 1964 w. w. BUCHMAN 3,163,799

EXPLODING SQUIRTED WIRE PULSED LIGHT SOURCE Filed April 26, 1962 WilliamW. Buchmon,

I/VVENTOR.

ATTORNEY.

United States Patent 3,163,799 EXPLODING SQUIRTED WIRE PULSED LIGHT.SOURCE William V. Buchman, 'Los Angeles, Calif., assignor to HughesAircraft Company, Culver City,Calif., a corporation of DelawareFiledAPr- 2. .5,. .96%, Sen N 1 2,, C aims- (C 14-122) This inventionrelates to an apparatus for producing pulses of intense light, such asthe type used to pump an optical maser or laser to the threshold forstimulated emission of coherent light from a body of laser material,high speed photography, etc., and particularly to an exploding Wire typeof pumping light source.

The exploding-wire light source is one of the most brillant lightsources known. It is cap-able of producing extremely high energy inputswhen applied to pumping lasers, for example. It gives high-peak powerlevels and extremely fast rise times. These are important factors indesigning high-power pulsed lasers for operations where short pulses ofvery intense pumping light are required, and in supplying the light forhighspeed cameras.

Efiicient coupling of energy is achieved by focusing the small diameter,line source light output of the exploding wire with a polishedelliptical mirror onto the body of laser material, such as a pink rubyrod. To eliminate the shock wave set up by the exploding wire at highenergy levels, the laser rod is surrounded by concentric hollowcylinders of plastic and glass. These help absorb the shock, filter outextraneous radiation that isnt useful for pumping, and prevent the rubysshattering from shock or wire fragments. To date, Nichrome, aluminum,copper and tungsten wire have been exploded from capacitor banks with anoutput energy capacity of about 33,600 joules.

For high-powered pulse laser operation, short bursts of very intensepumping light are needed. Since high power output is one of the mostsought-for goals in laser research, exploding Wire pumping appears to beone of the useful approaches for reaching it.

Among the problems'encountered in applying the exploding wire pumpinglight source to pulse laser operation, is the problem of repeatabilityat extremely high rates. This entails continuously feeding increments ofwire into the wire exploding means during extremely short increments oftime and continuously exploding the wire without loss of a significantamount of time.

Accordingly, it is an important object of this invention to provide amethod and means for continuously supplying, at extremely high rates, anincrement of metal wire to an exploding zone.

Additional objects will become apparent from the following description,which is given primarily for purposes of illustration, and notlimitation.

Stated in general terms, the objects of this invention are attained byproviding an exploding wire light source which includes a body of liquidelectrical conducting material, or molten metal, in a suitable, enclosedcontainer provided with an orifice and activator means, such as a pistonand cylinder arrangement, for example, for applying a pressure pulseupon the body of molten metal so that a jet or stream of the liquidconductor is formed outside the orifice. The jet of liquid conductor isejected into exploding-wire means, such as a capacitor, for example,adapted to explode the jet or stream of liquid conductor and produce apulse of very intense light.

A more detailed description of a specific embodiment of the invention,as applied to pumping a pink ruby laser, is given below with referenceto the appended drawing,

vwherein is given schematically a vertical sectional view showing a bodyof molten metal in a heated container 3,163,799 a en e Dec 9 1964 iceprovided with an orifice and a pressure actuator, adjacent a capacitor.

The device shown includes an orifice 10 formed in-the outer end of anozzle or jet 19. The inner end of nozzle 19 s bmers di a ody f uid c nu uch as molten metal 11, enclosedpressure-tight in a container ,17.Container 17 is made of a suitable'electrical conducting material, suchas a high melting point metal. A cy n e 13, it a p to 2 tt d' he ein s.att to, or made integral with, the cgntainer; 17 to exert pressure uponliquid metal 11, enclosed in the container. A suitable heater 18, suchas an electrical heater, is employed to maintain liquid metal 11 molten,in cases where that is necessary.

In operation, a jet of molten metal, such as Woods metal, tin lead,bismuth mercury, sodium, etc., alloys of such metals, molten salts, orother suitable liquid electrical conducting material, is squirted in afine stream through the orifice 10, by the application of a pressurepulse to liquid 11 through piston and cylinder arrangement 12, 13.Molten salts and conducting solutions can be used with different degreesof effectiveness. High temperatures require the use of materials thatcan withstand them. Reactive metals such as sodium require otherprecautions; such as perhaps requiring operation in a vacuum. Operationin a vacuum has the advantage of passing ultraviolet radiation. A liquidsuch as mercury breaks up into fine droplets, but even so the reductionof electrical resistance in the stream of droplets directs the explosion. In some cases, such as mercury, the toxicity of the explosionproducts require the addition of suitable means to confine the products.An advantage of a material like mercury squirted in a vacuum is that itcollects on the walls and flows back into a collecting reservoir (notshown) for reuse.

The jet of metal, or other conducting liquid, produced as described inthe paragraph above, is directed at an electrode 14, connected through aconductor 15, to the ungrounded side of a charged capacitor bank (notshown). The grounded side of the capacitor bank, which is the top of thecontainer 17, forms the other electrode 16. The electrode 16 isgrounded, as indicated at 20, and is connected to the conducting liquid11 through enclosed conducting container 17. Liquid 11 is maintained ina molten state by an electric heater 18, if necessary.

When the circuit is completed through the jet or stream of conductingliquid, an explosion of the jet, or Wire, takes place with a brilliantflash of intense light. The above sequence of steps can be carried outcontinuously, at an extremely rapid rate, to produce a series of rapid,short, intense light pulses which produce a corresponding series ofpulses of emitted coherent light from a laser beng pumped by theexploding liquid wire apparatus of this invention.

In general, the diameter of orifice 10 is made relatively small toproduce a fine stream, or jet, of conducting liquid,

which in turn results in a relatively high impedance squirted wire. Highimpedance is desirable, in general, for impedance matching to thecapacitor bank.

The piston 12 can be actuated in any desired, suitable manner. Forexample, it can be actuated by the use of a cam, solenoid, piezoelectriccrystal, hammer, hydraulically, pneumatically, or in any other suitablemanner.

What is claimed is:

1. An exploding-wire light source which comprises:

(a) a body of liquid electrical conductor;

(b) container means for enclosing the body of liquid electricalconductor;

(c) an orifice means immovably mounted in the container means andestablishing communication between the body of liquid electricalconductor and the exterior of the container means;

(d) an activator means for applying a pressure pulse upon the body ofliquid electrical conductor and forming a jet thereof by ejection ofliquid conductor through the orifice means; and

(e) electrical wire-exploding means for exploding the wire-jet of liquidelectrical conductor.

2. An exploding-wire light source which comprises:

(a) a body of molten metal;

(b) container means for enclosing the body of molten metal;

(c) an orifice means immovably mounted in the container means andestablishing communication be tween the body of molten metal and theexterior of the container means;

4 (d) an activator means for applying a pressure pulse upon the body ofmolten metal and forming a jet thereof by ejection of metal through theorifice means; and (0) electrical wire-exploding means for exploding thewire-jet of molten metal.

References Cited in the file of this patent UNITED STATES PATENTS SuitsJuly 16, 1940

1. AN EXPLODING-WIRE LIGHT SOURCE WHICH COMPRISES: (A) A BODY OF LIQUIDELECTRICAL CONDUCTOR; (B) CONTAINER MEANS FOR ENCLOSING THE BODY OFLIQUID ELECTICAL CONDUCTOR; (C) AN ORIFICE MEANS IMMOVABLY MOUNTED INTHE CONTAINER MEANS AND ESTABLISHING COMMINICATION BETWEEN THE BODYLIQUID ELECTRICAL CONDUCTOR AND THE EXTERIOR OF THE CONTAINER MEANS; (D)AN ACTIVATOR MEANS FOR APPLYING A PRESSURE PULSE UPON THE BODY OF LIQUIDELECTRICAL CONDUCTOR AND FORMING A JET THEREOF BY EJECTION OF LIQUIDCONDUCTOR THROUGH THE ORIFICE MEANS; AND (E) ELECTRICAL WIRE-EXPLODINGMEANS FOR EXPLODING THE WIRE-JET OF LIQUID ELECTRICAL CONDUCTOR.